Well, first let me say how sorry I am to know that you are suffering from Migraine Headaches.
My wife suffers from them everyday, and believe me when her headaches come, her day is pretty messed up for at-least several hours.
As for the Sleep Apnea, I suffer from them also. I was diagnose with sleep Apnea while on Active Duty, which I see you were too.
As for the rating, it's an automatic 50% disability rating from the VA, of course you will have to use a CPAP for the rest of your life which will help you sleep better at nights.
Problem is, it sucks trying to get used to the machine, but with time, and determination you should over come the anxiety that comes while getting used to it.
I wish you well, and I hope your claim is decided in your favor in a timely matter. Good Luck, and God Bless.
Aggie